Field
This disclosure relates to colour conversion.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, is neither expressly or impliedly admitted as prior art against the present disclosure.
Digital images or video signals represent images in a “colour space”. This defines the set or gamut of colours which can be expressed by that signal, as well as defining a combination of colours representing pure primary colours and white, for example.
A number of different colour spaces have been defined. A colour space which can be handled by an item of equipment might be defined with respect to a theoretically available colour space such as the so-called CIE 1931 colour space. For example, a so-called Rec 709 colour space provides a 36% coverage of the CIE 1931 space, whereas a so-called Rec 2020 colour space provides a rather greater 76% coverage of the CIE 1931 colour space.
This means that there are colours in the Rec 2020 space which are not representable in the Rec 709 space. But note that problem this can occur even where one colour space is not in fact larger than another; there can still be colours representable in one colour space which are not representable in the other colour space.
There is therefore a general need to convert from one colour space to another. For example, a modern camera might capture images (such as images forming part of a video signal) according to the Rec 2020 colour space, but these might need to be displayed on a Rec 709 display.